Greek officials have admitted that friction with international creditors was such it was unlikely a package of austerity cuts that have been set as the price of further aid would be approved by the Athens parliament before mid-November.

At no other time has near-bankrupt Greece so needed the €31.5bn (£25bn) in rescue funds dependent on the measures. With public coffers set to run dry by the end of November, the country could be forced to default on its debt mountain if there are further delays in the disbursement, put on hold since July.

The setback on Monday, the latest in four often tumultuous months of tortuous negotiations with the country's "troika" of lenders – the European Union, the European Central Bank and the International Monetary Fund – has highlighted the difficulty in drafting draconian spending cuts so fiercely opposed by unions and political forces in a country already hit by record levels of unemployment and poverty.

"They are pushing us to the absolute brink," said one high-ranking official at the labour ministry. "They don't just want our jacket but our shirt," he said, adding that Greece has already reduced its unit labour costs by a dramatic 15%.

With what the state-run TV channel NET called "open fronts" on all the main issues – including demands for up to 15,000 civil servants to be laid off immediately – it is now unlikely that the €13.5bn package of cuts will be approved by the Greek parliament before the next meeting of eurozone finance ministers on 12 November.

For the first time since assuming the post in June, Athens' technocrat finance minister, Yiannis Stournaras, looked unusually downbeat as he emerged from talks with the prime minister, Antonis Samaras, and attributed the latest hurdle to the "tremendous amount of work" that the negotiations entail.

The conservative leader, whose fragile coalition reached a "basic agreement" on the measures last month, had hoped to attend his first EU summit on Thursday with the talks behind him and the package agreed. In an interview at the weekend, he confidently predicted that "we will have fully completed the agreement on the fiscal and structural prior actions for the disbursement" by the summit.

Addressing a business conference in Athens, the socialist Pasok leader, Evangelos Venizelos, said the financial lifeline was crucial for an economy about to enter a sixth year of recession and "for a society that has reached its limits". Around €25bn of the cash injection will be used to recapitalise banks in the hope of re-energising Greece's cash-starved economy.

The endless foot-dragging has exacerbated a fiscal and structural reform programme that is already badly off track. Missed targets have produced a "financing gap" that also appears to have added to the pressure of finalising the package.

The IMF announced last week that Greece's debt looked set to increase from 170.7% of GDP to nearly 182% in 2013 – despite private sector creditors already taking a huge hit on Greek bonds.

The pessimism has added to the difficulty in making headway amid signs that lenders are reluctant to meet demands by the Samaras government for a two-year extension to the fiscal consolidation programme before the country commits to further reforms. Indicative of the frustration the stalled talks have produced, the Swedish finance minister, Anders Borg, raised the spectre of a Greek exit from the eurozone in the coming months. "It's most probable that they will leave. We shouldn't rule out this happening in the next half year," he said, adding that a "Grexit" would not alarm financial markets.